Art of refining hydrocarbons



Aug. 22, 1933; Q KAA A a 1,923,150

-ART OF REFINING HYDROCARBONS Filed Aug 15. 19:51

HNVENTOR Or/fl 6' Haasa Patented Aug. 22, 1933 UNITED STATES ART OFREFINING HYDROCARBONS rinG. Kaasa, Munster, Ind., assignorto SinclairRefining Company, New York, .N. Y., a

Corporation of Maine Application August 15, 1931. Serial No. 557,250

1 Claim.

This invention relates to improvements in the cracking of refractorypetroleum stocks to produce gasoline. Operations of this character areconventionally carried out by heating the refractory stock to a highcracking temperature while in transit through externally heated tubesserially connected to form a long continuous heating passage. Theinvention relates particularly to operations of this character.

Coke, the solid decomposition product of the cracking reaction,deposited from a stream of relatively more refractory stock whilepassing through externally heated tubes in which it is heated to acracking temperature, is hard whereas a coke deposited from relativelyless refractory stock under similar conditions is soft. In properlycontrolled operations, the rate of deposition of hard coke is very slow,much slower than the rate of deposition of soft coke usuallyencountered, but eventually the accumulation of deposited coke requirestermination of the operation to permit cleaning of the externally heatedtubes. When cleaning becomes necessary, the hard coke deposited fromrefractory stock ren- 25 ders the cleaning operation particularlydiflicult. According to this invention, however, the cleaning operationis simplified by initially circulating a less refractory stock throughand heating it to a cracking temperature in the heated 30 tubes for arelatively short period, a minor part of the period of operation, beforecirculating the refractory stock therethrough. A thin deposit of softcoke is formed on the interior of the externally heated tubes duringthis initial period of operation and the hard coke deposited from therefractory stock in the subsequent period of operation is deposited uponthis previously formed deposit of soft coke instead of upon the interiorof the externally heated tubes. The soft coke itself does not involveany particular difiiculty ill the cleaning operation and, the thindeposit of soft coke being easily frangible, facilitates the removal, inthe cleaning operation, of the hard coke deposited thereon. 45- Theinitial period of circulation of less refractory stock through theexternally heated tubes is advantageously limited to avoid depositionduring this period of a coke deposit itself sufficient to interfere withthe operation. Usually, this initial period of operation isadvantageously limited to about 143% of the total period of operation.Heavy virgin gas oil, 32-34 A. P. I. gravity gas oil for example, is anadvantageous stock from which to form the initial deposit of soft coke.

The accompanying drawing illustrates one form of apparatus, of the manyforms of apparatus, in which the invention may be practiced. Theapparatus illustrated in the accompanying" drawing is of the generaltype described and 0 illustrated in Letters Patent Number 1,774,602,granted to Sinclair Refining Company Septembet 2, 1930 on an applicationof E. W. Isom and Eugene C. Herthel.

Referring to the drawing, a stream of stock to 5 g be cracked is forced,by means of pump 2, through a battery of serially connected tubesarranged'in a heating furnace 1 into the vapor separating receptacle 3from which vapors, including vapors of the cracked product, are takenoff to a frac- 7o tionating system, the stock to be cracked being heatedto a cracking temperature during passage through the heated tubes. Thestock to be cracked may be heated to a temperature approximating850-950" F., for example, and is discharged into the vapor separatingreceptacle 3. A pressure approximating 100-300 pounds per square inch,for example, may be maintained in the vapor separating receptacle 3, ora pressure approximating 1-10 pounds or a somewhat higher 30 pressure,for example, may be maintained in the vapor separating receptacle 3. Thepressure on the hot oil products discharged from the battery of heatedtubes may be maintained just sufficient to force these hot oil productsinto the vapor separating receptacle 3, or this pressure may bemaintained at some higher value, 300-600 pounds per square inch, forexample, and the pressure on these hot oil products reduced as they aredischarged into the vapor separating receptacle 3. It is intended andwill be understood that the foregoing details with respect to apparatusand operation are intended merely to illustrate one form of apparatusand operation in which the invention may be embodied.

In practicing the invention in conjunction with the operation of theapparatus illustrated in the accompanying drawing, if the regular periodof operation is 50-100 days (time on stream), for example, a heavy gasoil stock is 100 circulated through the battery of heated tubes for aninitial period of 1-3 days, for example, before circulation of therefractory stock, a kerosene character stock or a light gas oilcharacter stock, for example, through the battery of heated 9 tubes isbegun.

The invention is useful particularly in conjunction with pressuredistillation, or so-called pressure shell cracking operations in whichvapor separation is carried out under super- 9 atmospheric pressure, inconjunction with pressure digestion, or so-called reaction chamber,cracking operations in which vapor separation is carried out under lowerpressure following digestion under higher pressure, and in conjunctionwith operations in which stock to be cracked is heated to a crackingtemperature under high superatmospheric pressure and in which the hotoil products of this heating operation are separated into a vaporizedfraction and an unvaporv ized fraction under lower pressure or so-calledpressure coil" cracking operations.

I claim:

In the cracking of refractory petroleum stocks to produce gasoline inoperations in which the refractory stock is heated to a crackingtemperature while in transit through externally heated tubes, theimprovement which comprises initially circulating a stream of lessrefractory stock through and heating it to a cracking temperature in theheated tubes for a minor part of the period of operation until a thindeposit of soft coke is formed on the interior of the tubes andthereafter circulating a stream of the refractory stock through andheating it to a cracking temperature in the heated tubes whereby hardcoke deposited from the refractory stock is deposited upon thepreviously deposited soft coke.

ORIN G. KAASA.

